In order to accommodate the fast increase in image and video data in the current information driven society, increase in capacity and reduction in size of a data recording and reproducing apparatus is in progress. In the data recording and reproducing apparatus utilizing light, since the recording density depends on a light wavelength, the increase in density is achieved by utilizing light having a short wavelength. Shortening of the wavelength is limited and realization of recording density which does not depend on the wavelength has been searched for, and a technology including a method to localize light energy to a minute spot exceeding the diffraction limited of the light by utilizing near field light has received attention.
In the data recording and reproducing apparatus utilizing magnetism, in order to magnetize a minute area on a surface of a recording medium separately, a near field light assisted magnetic recording system in which only the minute area is heated by being irradiated with the near field light thereto to lower a coercive force thereof and then is magnetized is considered to be a promising next generation candidate of a recording and reproducing principle.
In a magnetic recording technology, a longitudinal recording system in which recording of data in the recording medium is achieved by magnetizing the minute area in a recording layer in the direction parallel to the surface of the recording medium has been employed in the related art. However, improvement in recording density has been difficult to achieve due to the problem of heat fluctuations. In order to solve this problem, employment of so-called a vertical recording system in which the minute area of the recording layer is magnetized in the vertical direction with respect to the surface of the recording medium has been employed. In this system, since the N-pole and the S-pole can hardly form a loop in the recording layer, it is stable in terms of energy, and has a resistance to heat demagnetization in comparison with the longitudinal recording system. In order to further improve the recording density, a material having a larger coercive force as the recording medium is employed in order to minimize a mutual-effect between adjacent magnetic domains or the heat fluctuations. Therefore, even with the vertical recording system described above, recording of data in the recording medium has been difficult to achieve.
Therefore, a system to magnetically record in the recording medium having a large coercive force by lowering the coercive force by heating the minute area momentary receives attention. This is a system in which an element which serves as a heat source is formed in the vicinity of a magnetic recording element mounted on an air floating slider and magnetization of a medium recording layer is inverted by the magnetic field generated by the magnetic recording element while heating the surface of the recording medium by heat irradiated from the heat source. Since the coercive force of the recording layer is large, the area which is magnetized once may exist stably with respect to the heat fluctuations when the temperature is lowered even when it is in the proximity of the next area. This is referred to as a heat assisted magnetic recording system. Important factors for increasing the recording density in the heat assisted magnetic recording system are to divide the area heated for assisting into minute areas, and to heat only areas in which recording is desired. As a method being able to switch ON and OFF at a high frequency and apply heat only an area of several to several tens nm, the above-described near field light may be utilized. This is referred to as the near field light assisted magnetic recording system. Reduction of areas of magnetic poles which generate the magnetic field is also important, and it is necessary to magnetize only the minute area in the heated area.
A head of the near field light assisted magnetic recording system has a structure having a near field light generating element adjacently to a recording magnetic pole of a magnetic head in the related art. The near field light generating element is a scatterer formed of, for example, a thin film metal, and generates a near field light in the minute area by being irradiated with a light from a laser (JP-A-2004-158067, (pp. 5-6, FIG. 1)).
A structure in which a metal thin film having a bow-tie shape (a shape having two triangle arranged with respective apexes oppose to each other) is formed on a bottom surface of the head, and a near field light is generated in a minute gap between the apexes of the triangles at a center of the bow-tie by irradiating the bow-tie with a light vertically from above, so that the near field light is generated superimposingly in an area having the strong magnetic field is also proposed. In the near field light assisted magnetic recording head, the near field light generating element is a bow-tie shaped plane metal film formed on the bottom surface of the head, and the light from the laser is introduced by an optical fiber or the like and reflected by a mirror to apply on the bow-tie, so that the near field light is generated in the gap at the center of the bow-tie. In addition, since the bow-tie serves also as the magnetic recording element, a medium surface area which is heated by the near field light matches the area to be magnetized by the magnetic field. Accordingly, dividing the minute spot by the near field light into the minimal area to the limit is enabled, which is suitable for high-density recording (JP-A-2002-298302 (pp. 4-6, FIG. 1)).
[Patent Document 1] JP-A-2004-158067
[Patent Document 2] JP-A-2002-298302
However, in the near field light assisted magnetic recording head in the structure in the related art, since the near field light generating element is formed adjacently to the magnetic recording element, and is configured in such a manner that an incident light from the laser is applied obliquely from the front of the head, the near field light generating element is arranged outside the magnetic recording element, that is, on an end side of the slider. An air floating head is configured to float obliquely with an air inflow end (leading edge) floating by a larger floating amount than an outflow end (trailing edge), and the magnetic recording element is needed to be brought into proximity to the surface of the recording medium to the maximum for the high-density recording. Therefore, it is mounted near the outflow end. Since the near field light generating element is located outside thereof, it is arranged always behind the magnetic recording element in terms of the scanning direction of the head when viewed from the medium as a result (Patent Document 1, FIGS. 1 to 4). In the near field light assisted magnetic recording for recording by the magnetic recording element after having heated the minute area on the surface of the medium by the near field light, the near field light generating element is preferably arranged in front of the magnetic recording element.
In the related art, since the near field light generating element is arranged behind the magnetic recording element, the area to be heated by the near field light is inevitably a wide area not only an area immediately below the near field light generating element, but also including the front thereof. Therefore, there is a problem such that a minute spot performance which the near field light generating element originally has cannot be demonstrated sufficiently. Also, in the near field light assisted magnetic recording head having the structure in the related art, incoming of the light into the near field light generating element is an air propagation from the laser, so that there is a difficulty in downsizing and simplification of an optically system.
Another near field light assisted magnetic recording head having the structure in the related art includes the bow-tie for generating both the near field light and the magnetic field formed of the plane film formed on the bottom surface of the head, the generated magnetic field is wide spread over the bow-tie. Although the gap at the center of the bow-tie defines the recording density in the case of the longitudinal recording system, the size of a portion of a main magnetic pole opposing the medium defines the recording density in the case of the vertical recording. When the bow-tie is viewed from the side of the recording medium, since the main magnetic pole corresponds to the entire portion of one side of the bow-tie, it is necessary to make the bow-tie by itself to be minute in order to increase the recording density. When the size of the bow-tie is reduced, a periphery of the bow-tie is included in an incident light spot, and the near field light is generated not only at a center portion of the bow-tie, but also in the periphery thereof, so that an erroneous recording may be resulted in the periphery of the bow-tie. In this manner, the head having a structure in which a strong recording magnetic field is generated only at the center portion of the bow-tie where the near field light exists locally is needed.
In view of such points, it is an object of the present invention to provide a near field light assisted magnetic recording head in which wide-spreading of a near field light and a magnetic field is restrained so that a writing reliability is improved, and a recording apparatus using the same.